How to reduce the output video size?
AVI is both large and not the most common format. It is generally played natively only on Windows, although other software packages can also open it (such as VLC). As such, it is not a good choice.

The format you are looking for is MP4 with the H.264 codec. It is the most common format and codec that plays on almost everything. It also has a relatively small file size.



As an additional tip, you should watch this tutorial on the best practice for rendering animations (you should render the individual frames as PNG images first, then encode the frames into a video file).